[PATCH 5/6] drm: Do not attempt to round_up() zeros in drm_suballoc_try_alloc()

[Krzysztof Karas]

Due to the nature of round_up(), its first argument is
decremented by one. drm_suballoc_hole_soffset() may return 0,
which is then passed to round_up() and may wrap around.
Remedy that by adding a guard against that value.

Fixes: 849ee8a2f0df ("drm/suballoc: Extract amdgpu_sa.c as generic 
suballocation helper")
Cc: Maarten Lankhorst <maarten.lankho...@linux.intel.com>
Cc: <sta...@vger.kernel.org> # v6.4+
Signed-off-by: Krzysztof Karas <krzysztof.ka...@intel.com>
---
 drivers/gpu/drm/drm_suballoc.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/drm_suballoc.c b/drivers/gpu/drm/drm_suballoc.c
index 879ea33dbbc4..7f01e9d9fcfd 100644
--- a/drivers/gpu/drm/drm_suballoc.c
+++ b/drivers/gpu/drm/drm_suballoc.c
@@ -165,11 +165,13 @@ static bool drm_suballoc_try_alloc(struct 
drm_suballoc_manager *sa_manager,
                                   struct drm_suballoc *sa,
                                   size_t size, size_t align)
 {
-       size_t soffset, eoffset, wasted;
+       size_t soffset, eoffset, wasted = 0;
 
        soffset = drm_suballoc_hole_soffset(sa_manager);
        eoffset = drm_suballoc_hole_eoffset(sa_manager);
-       wasted = round_up(soffset, align) - soffset;
+
+       if (soffset)
+               wasted = round_up(soffset, align) - soffset;
 
        if ((eoffset - soffset) >= (size + wasted)) {
                soffset += wasted;
-- 
2.34.1